Note that it returns the encoding ID, not a symbolic
string such as EUC_JP. To convert
an encoding ID to an encoding name, you can use:

char *pg_encoding_to_char(int encoding_id);

PQsetClientEncoding

Sets the client encoding.

int PQsetClientEncoding(PGconn *conn, const char *encoding);

conn is a connection to
the server, and encoding is
the encoding you want to use. If the function successfully
sets the encoding, it returns 0, otherwise -1. The current
encoding for this connection can be determined by using
PQclientEncoding.

PQsetErrorVerbosity

Determines the verbosity of messages returned by
PQerrorMessage and
PQresultErrorMessage.

PQsetErrorVerbosity sets
the verbosity mode, returning the connection's previous
setting. In TERSE mode, returned
messages include severity, primary text, and position only;
this will normally fit on a single line. The default mode
produces messages that include the above plus any detail,
hint, or context fields (these might span multiple lines).
The VERBOSE mode includes all
available fields. Changing the verbosity does not affect
the messages available from already-existing PGresult objects, only
subsequently-created ones.

PQtrace

Enables tracing of the client/server communication to a
debugging file stream.

void PQtrace(PGconn *conn, FILE *stream);

Note: On Windows, if the libpq library and an application
are compiled with different flags, this function call
will crash the application because the internal
representation of the FILE
pointers differ. Specifically,
multithreaded/single-threaded, release/debug, and
static/dynamic flags should be the same for the library
and all applications using that library.